Unit for and method of registering/feeding paper and image forming apparatus using the same

ABSTRACT

A paper registering/feeding unit that registers a sheet of print paper and feeds it to a printing unit, a method of registering/feeding a sheet of print paper, and an image forming apparatus using the same are provided. A paper registering/feeding unit includes a rotatable pick-up roller including an effective contact surface which contacts a sheet of print paper to pick up the print paper. The paper registering/feeding unit also includes a pair of registration rollers in contact with each other to form a nip along the pathway of the print paper, a sensor sensing the approach of the front end of the print paper picked up by the pick-up roller toward the nip of the registration rollers, and a controller that controls a rotation of the registration rollers based on a time of sensing the end of the print paper by the sensor.

CROSS-REFERENCE TO RELATED PATENT APPLICATION

This application claims the benefit under 35 U.S.C. § 119(a) of Korean Patent Application Nos. 10-2005-0048429 and 10-2005-95529, filed on Jun. 7, 2005 and Oct. 11, 2005, respectively, in the Korean Intellectual Property Office, the entire disclosures of which are hereby incorporated by reference.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to an image forming apparatus. More particularly, the present invention relates to an image forming apparatus including a paper registering/feeding unit that registers a sheet of print paper and feeds the paper to a printing unit, and a method of registering/feeding the same.

2. Description of the Related Art

An image forming apparatus prints an image on a sheet of print paper. The image forming apparatus includes a printing unit that forms an image on a sheet of print paper and a paper registering/feeding unit that picks up, registers, and feeds a sheet of print paper to the printing unit.

FIG. 1 is a schematic sectional view of a conventional paper registering/feeding unit 10. Referring to FIG. 1, the conventional paper registering/feeding unit 10 includes a paper feed cassette 11 into which sheets of print paper P are loaded, a pick-up roller 12 that picks up a sheet of the print paper P from the paper feed cassette 11, a pair of paper feeding rollers 15 that transport the print paper P picked up by the pick-up roller 12, and a pair of registration rollers 25 that register the front end of the print paper P transported by the paper feeding rollers 15. In addition, the conventional paper registering/feeding unit includes a lever 21 and a photo sensor 20 positioned on the pathway of the print paper P before the registration rollers 25.

When the front end of the print paper P picked up by the pick-up roller 12 and transported, preferably upwardly, toward the registration roller 25 by the paper feeding rollers 15, the print paper P pushes the lever 21 and the photo sensor 20 generates a sensing signal which corresponds to the front end of the print paper P. The sensing signal is transmitted to a controller (not illustrated). The controller controls the paper feeding rollers 15 to pause transportation of the print paper P when a nip N of the registration rollers 25 hinders transportation of the front portion of the print paper P and a curl C is formed on the front portion of the print paper P. The controller pauses transportation of the print paper P after a predetermined time-lag from a time of sensing the front end of the print paper P. The front end of the print paper P is registered via the the curl C formation during standby for printing. Then, the print paper P is transported again to a printing unit (not illustrated) by the rotation of the registration rollers 25 and the paper feeding rollers 15.

There are drawbacks with the conventional unit. Since the conventional paper registering/feeding unit 10 uses the paper feeding rollers 15 between the pick-up roller 12 and the registration rollers 25, it has a relatively complicated structure, high manufacturing costs, and limits the minimization of the image forming apparatus.

Accordingly, there is a need for an improved paper registering/feeding unit which does not position paper feeding rollers between a pick-up roller and registration rollers and an image forming apparatus having the same.

SUMMARY OF THE INVENTION

An aspect of the present invention is to solve at least the above problems and/or disadvantages and to provide at least the advantages described below. Accordingly, an aspect of the present invention is to provide a paper registering/feeding unit that does not use paper feeding rollers between a pick-up roller and registration rollers and an image forming apparatus having the same.

The exemplary embodiments of the present invention also provide a method of registering/feeding a print paper using the paper registering/feeding unit.

According to an aspect of the present invention, there is provided a paper registering/feeding unit including a rotatable pick-up roller including a contact surface which contacts a sheet of print paper to pick up the print paper. The paper registering/feeding unit also includes a pair of registration rollers in contact with each other form a nip along the pathway of the print paper, a sensor sensing the approach of the front end of the print paper picked up by the pick-up roller toward the nip of the registration rollers, and a controller that controls the rotation of the registration rollers based on the time of sensing the front end of the print paper by the sensor. The length of the arc of the contact surface is greater than the distance between the pick-up roller and the nip of the registration rollers along the pathway of the print paper.

The controller may have a unit that rotates the registration rollers after a first time-lag from a time of sensing the front end of the print paper so that the front end of the print paper is curled, registered and passed through the nip of the registration rollers, and that pauses the registration rollers after a second time-lag from the time of sensing the transportation of the front end of the registered print paper passing through the nip so that the front end of the print paper is discontinued and on standby for printing.

The paper registering/feeding unit may include no additional rollers for feeding print paper between the pick-up roller and the registration rollers.

The paper registering/feeding unit may further include a clutch that selectively connects and disconnects the registration rollers to and from a driving source for driving the registration rollers according to control signals generated by the controller.

According to another aspect of the present invention, there is provided an image forming apparatus having a printing unit that print an image on print paper and a paper registering/feeding unit that registers and feeds the print paper to the printing unit. The paper registering/feeding unit includes a rotatable pick-up roller inlcuding a contact surface which contacts a sheet of print paper to pick up the print paper. The paper registering/feeding unit also includes a pair of registration rollers in contact with each other forming a nip along the pathway of the print paper, a sensor sensing the approach of the front end of the print paper picked up by the pick-up roller toward the nip of the registration rollers, and a controller that controls the rotation of the registration rollers based on the time of sensing the front end of the print paper P by the sensor. The length of the arc of the contact surface is greater than the distance between the pick-up roller and the nip of the registration rollers along the pathway of the print paper.

The controller may have a unit that rotates the registration rollers after a first time-lag from the time of sensing the front end of the print paper so that the front end of the print paper is curled, registered and passed through the nip of the registration rollers, and that pauses the registration rollers after a second time-lag from the time of sensing the front end of the registered print paper passing through the nip so that the transportation of the front end of the print paper is discontinued and on standby for printing.

The image forming apparatus may include no additional rollers for feeding the print paper between the pick-up roller and the registration rollers.

The image forming apparatus may further include a clutch that selectively connects and disconnects the registration rollers to and from a driving source for driving the registration roller according to control signals generated by the controller.

According to still another aspect of the present invention, there is provided a method of registering/feeding print paper, including picking up and transporting print paper toward a nip of registration rollers by rotating a pick-up roller. The method also includes the steps of sensing the approach of the front end of the print paper toward the nip, driving the registration rollers after a first time-lag from a time of sensing the front end of the print paper so that the front end of the print paper is curled, registered and passed through the nip of the registration rollers, and pausing the registration rollers after a second time-lag from the time of sensing the front end of the print paper toward the nip so that the transportation of the front end of the print paper registered and passed through the nip is discontinued and on standby for printing.

In the transporting of the print paper, the print paper may be directly transported to the nip of the registration rollers by only the transportation force of the pick-up roller.

According to yet another aspect of the present invention, there is provided a paper registering/feeding unit including a rotatable pick-up roller that has an effective contact surface which contacts a sheet of print paper to pick up the print paper. The paper registering/feeding unit also includes a pair of registration rollers in contact with each other to form a nip along the pathway of the print paper, a sensor sensing the approach of the front end of the print paper picked up by the pick-up roller toward the nip of the registration rollers, and a controller that controls a rotation of the registration rollers based on a time of sensing the front end of the print paper by the sensor. The length of the arc of the effective contact surface is greater than the distance between the position where the pick-up roller initially contacts the print paper for feeding and the nip of the registration rollers along the pathway of the print paper.

The controller may include a unit that rotates the registration rollers after a first time-lag from the time of sensing the front end of the print paper so that the front end of the print paper is curled, registered and passed through the nip of the registration rollers, and that pauses the registration rollers after a second time-lag from the time of sensing the front end of the registered print paper passing through the nip so that the transportation of the front end of the print paper is discontinued and on standby for printing.

The paper registering/feeding unit may include no additional rollers for feeding the print paper between the pick-up roller and the registration rollers.

The image forming apparatus further includes a clutch that selectively connects and disconnects the registration rollers to and from the driving source for driving the registration roller according to control signals generated by the controller.

According to further another aspect of the present invention, there is provided an image forming apparatus having a printing unit that prints an image on print paper and a paper registering/feeding unit that registers and feeds the print paper to the printing unit. The paper registering/feeding unit includes a rotatable pick-up roller including an effective contact surface which contacts a sheet of print paper to pick up the print paper. The paper registering/feeding unit also includes a pair of registration rollers in contact with each other to form a nip along the pathway of the print paper, a sensor sensing the approach of the front end of the print paper picked up by the pick-up roller toward the nip of the registration rollers, and a controller that controls rotation of the registration rollers based on a time of sensing the front end of the print paper by the sensor. The length of the arc of the effective contact surface is greater than the distance between the position where the pick-up roller initially contacts the print paper for feeding and the nip of the registration rollers along the pathway of the print paper.

The controller may includes a unit that rotates the registration rollers after a first time-lag from the time of sensing the front end of the print paper so that the front end of the print paper is curled, registered and passed through the nip of the registration rollers, and that pauses the registration rollers after a second time-lag from the time of sensing the front end of the registered print paper passing through the nip so that the transportation of the front end of the print paper is discontinued and on standby for printing.

The image forming apparatus may include no additional rollers for feeding print paper between the pick-up roller and the registration rollers.

The paper registering/feeding unit further includes a clutch that selectively connects and disconnects the registration rollers to and from the driving source for driving the registration roller according to control signals generated by the controller.

Other objects, advantages, and salient features of the invention will become apparent to those skilled in the art from the following detailed description, which, taken in conjunction with the annexed drawings, discloses exemplary embodiments of the invention.

BRIEF DESCRIPTION OF THE DRAWINGS

The above and other objects, and features, and advantages of certain exemplary embodiments of the present invention will be more apparent from the following description taken in conjunction with the accompanying drawings, in which:

FIG. 1 is a schematic sectional view of a conventional paper registering/feeding unit;

FIG. 2 is a schematic sectional view of an image forming apparatus according to an exemplary embodiment of the present invention;

FIG. 3 is a perspective view of a pick-up roller and a knock-up plate of FIG. 2;

FIGS. 4 through 7 are schematic views sequentially illustrating an operation of the paper registering/feeding unit of FIG. 2; and

FIGS. 8 through 11 are schematic views sequentially illustrating an operation of the paper registering/feeding unit according to another embodiment of the present invention.

Throughout the drawings, the same drawing reference numerals will be understood to refer to the same elements, features, and structures.

DETAILED DESCRIPTION OF EXEMPLARY EMBODIMENTS

The matters defined in the description such as a detailed construction and elements are provided to assist in a comprehensive understanding of the exemplary embodiments of the invention. Accordingly, those of ordinary skill in the art will recognize that various changes and modifications of the embodiments described herein can be made without departing from the scope and spirit of the exemplary embodiments of the invention. Also, descriptions of well-known functions and constructions are omitted for clarity and conciseness.

FIG. 2 is a schematic sectional view of an image forming apparatus 100 according to an exemplary embodiment of the present invention. Referring to FIG. 2, the image forming apparatus 100 is an electro-photographic type image forming apparatus, which supplies a developer, such as toner, to an electrostatic latent image formed on an outer circumference of a photosensitive medium by light scanning, develops the electrostatic latent image into a visible image using the toner, and transfers and fuses the visible image onto a sheet of print paper P, thereby printing a desired image. The image forming apparatus 100, in which a sheet of print paper P is preferably upwardly transported along a roughly c-type pathway R for the print paper P, includes a printing unit and a paper registering/feeding unit for registering and feeding the print paper P to the printing unit. The paper registering/feeding unit is positioned inside a case 101. The printing unit includes a removable developer unit 110 inserted in the case 101, a fixing unit 130, a transfer roller 125, and light scanning unit 127.

The developer unit 10 includes a housing 111 in which a developer, such as toner is stored. The developer unit 110 also includes a photosensitive medium 115 on which an electrostatic latent image is formed by light scanning, a charging roller 113 that charges the photosensitive medium 115, and a waste toner cleaner 114 that removes waste toner residues from the photosensitive medium 115′. The developer unit 110 further includes a developing roller 117 that develops an image on the outer circumference of the photosensitive medium 115 by supplying the toner to an electrostatic latent image formed on the outer circumference of the photosensitive medium 115, a doctor blade 118 that controls the thickness of the toner attached on the surface of the developing roller 117, and a supplying roller 119 that supplies the toner to the developing roller 1 17. In addition, the housing 111 includes an agitator 121 that agitates the toner to prevent hardening. The developer unit 110 is preferably of a cartridge type and can be replaced with a new one when the developer therein is exhausted.

The transfer roller 125 is positioned to form a transfer nip Nt by contacting the photosensitive medium 115 and presses the print paper P onto the photosensitive medium 115. Therefore, a visible image developed on the outer circumference of the photosensitive medium 115 can be transported onto the print paper P passing through the transfer nip Nt.

The fixing unit 130 includes a heat roller 131 and a pressure roller 133 which face each other. When a sheet of print paper P on which the visible image is transferred passes through a gap between the heat roller 131 and the pressure roller 133, the visible image is printed on the print paper P by heat and pressure. A plurality of paper discharging rollers deliver the image printed paper P to a paper tray 102 outside the case 101 and are mounted above the fixing unit 130.

The paper registering/feeding unit 140 includes a paper feed cassette 141 in which sheets of print paper P are loaded, a pick-up roller 150 having a semicircular surface, and a friction pad 147 which contacts a contact surface 151 of the pick-up roller 150. Consequently, a sheet of printing paper P is picked up. The paper registering/feeding unit also includes a first and second registration rollers 161 and 163 that registers and feeds the print paper P picked up to the printing unit; a photo sensor 165 that senses the approach of the print paper P; and a lever 167.

The printing process of the image forming apparatus 100 having the above-described structures is as follows. The photosensitive medium 115 is charged to a predetermined electric potential by the charging roller 113 and induced by scanning light L from the light-scanning unit 127. Thus, an electrostatic latent image corresponding to an image to be printed is formed on the outer circumference of the photosensitive medium 115. A toner stored in the housing 111 is supplied to the photosensitive medium 115. Then, the electrostatic latent image is formed thereon by a supply roller 119 and a developing roller 117 and a visible image is developed on the outer circumference of the photosensitive medium 115. Meanwhile, a sheet of print paper P is picked up by the pick-up roller 150, registered and fed by the pair of registration rollers 161 and 163, and passes through the transfer nip Nt between the photosensitive medium 115 and the transfer roller 125. Here, the visible image developed on the outer circumference of the photosensitive medium 115 is transferred onto the surface of the print paper P facing the photosensitive medium 115. The image transferred onto the print paper P is fixed on the print paper P by heat and pressure while passing through a fixing unit 130. Lastly, the paper is delivered by a pair of paper discharging rollers 135 and stacked on the paper tray 102.

FIG. 3 is a perspective view of a pick-up roller 150 and a knock-up plate 142 of FIG. 2. Referring to FIGS. 2 and 3, the knock-up plate 142, on which sheets of print paper P are loaded, is attached to the inside of the removable paper feed cassette 141 inserted into the case 101 by hinges 143. The knock-up plate 142 is elevated in accordance with the rotation of the pick-up roller 150. The elevation unit of the knock-up plate 142 includes springs 145 that elastically bias the knock-up plate 143 in the upward direction. The elevation unit also includes a pair of cams 157 which are joined at both ends of a shaft 153 of the pick-up roller 150 and rotated together with the pick-up roller 150.

Prior to the input of a print command into the image forming apparatus 100, as shown in FIG. 3, the cams 157 press either edge of the front end of the knock-up plate 142 so that print paper P is separated from the pick-up roller 150. When a print command is input into the image forming apparatus 100, the cam 157 is rotated together with the pick-up roller 150 due to the rotation of the shaft 153. Therefore, the cam 157 does not press both edges of the front end of the knock-up plate 142. Accordingly, the front end of the knock-up plate 142 is moved up by the elastic force of the spring 145, and thus a front end Pt of a sheet of paper P loaded on the knock-up plate 142 contacts with the contact surface 151 of the rotating pick-up roller 150. A plurality of pick up ancillary rollers 155 are placed to freely rotate on the shaft 153. The pick up ancillary rollers 155 assist in transporting the print paper P sheet by sheet.

FIGS. 4 through 7 are schematic views sequentially illustrating the operation of the paper registering/feeding unit 140 of FIG. 2. Referring to FIGS. 4 through 7, the paper registering/feeding unit 140 does not include an additional roller for feeding the print paper P between the pick-up roller 150 and the pair of the registration rollers 161 and 163. A sheet of print paper P is transported toward the nip N of the registration roller 161 and 163 by a frictional force of the pick-up roller 150. In order for the front end Pt of the picked up print paper P to reach the nip N, the arc length d1 of the contact surface 151 is greater than the distance d2 of a pathway R1 which is a portion of the entire pathway R (see FIG. 2) of the print paper. The pathway R1 is from the position where the contact surface 151 is separated from the friction pad 147 to the nip N. Specifically, the portion R1 begins from the separation point of the contact surface 151 and the friction pad 147 and ends at the nip N.

Meanwhile, the first registration roller 161 is rotated by a driving force of a driving source like a motor (not illustrated), while the second registration roller 163 is a passive roller that contacts the first registration roller 161, forms a nip N with the first registration roller 161, and is rotated by the first registration roller 161. The motor is connected to the first registration roller 161 via an electronic clutch 175, such as a power switching unit. The electronic clutch 175 selectively connects and disconnects the first registration roller 161 to and from the motor. The motor and the electronic clutch 175 are generally known to those of ordinary skill in the art, and thus a detailed description thereof will be omitted for clarity and conciseness.

The lever 167 includes one end 167 a blocking a front end Pt of the print paper P transported toward the nip N and the other end 167 b extended toward the photo sensor 165. The lever 167 can be rotated on a predetermined pivot shaft 168 located between the one end 167 a and the other end 167 b. Since the lever 167 is elastically biased, the lever 167 is pushed by the front end Pt of the print paper P transported toward the nip N to rotate clockwise on the pivot shaft 168, and then may return to the initial position after the tail end of the print paper P passes through the one end 167 a of the lever 167. The rotation angle of the lever 167 may be limited by a stopper (not illustrated).

The photo sensor 165 includes a slit (not illustrated) which allows the other end 167 b of the lever 167 to pass through it. The inner wall of the slit includes a light emitter (not illustrated) that radiates a laser and a light receiver (not illustrated) that receives the radiated laser. The photo sensor 165 is generally known to those of ordinary skill in the art, and thus a detailed description thereof will be omitted.

The paper registering/feeding unit 140 includes a controller 170 that controls the rotation of the registration rollers 161 and 163 with respect to a time of sensing the front end Pt of the print paper P by the photo sensor 165. The controller 170 is electrically connected to the photo sensor 165 to receive the sensing signal of the front end Pt of the print paper P from the photo sensor 165. The controller 170 is also electrically connected to the electronic clutch 175 to transmit a control signal to the electronic clutch 175 to control the rotation of the registration rollers 161 and 163.

Hereinafter, the operation of the registering/feeding unit 140 having the above-described structures will be described.

When a print command is input to the image forming apparatus 100, (see FIG. 2), the pick-up roller 150 is rotated to pick up a front end Pt of the print paper P and transports the print paper P to reach the nip N of the registration roller 161 and 163. As shown in FIG. 4, the one end 167 a of the lever 167 positioned below the nip N blocks the pathway R1 of a sheet of the print paper P. The other end 167 b of the lever 167 is positioned in the slit (not illustrated) of the photo sensor 165. Light emitted by the light emitter (not illustrated) of the photo sensor 165 is blocked by the other end 167 b and cannot reach the light receiver (not illustrated). The electronic clutch 175 disconnects the motor (not illustrated) and the first registration roller 161 according to a pause control signal transmitted by the controller 1701. Therefore, the first and second registration rollers 161 and 163 do not rotate.

When the front end Pt of the print paper P is upwardly transported to push up the one end 167 a of the lever 167, as shown in FIG. 5, the lever 167 is rotated clockwise on the pivot shaft 168, and then the other end 167 b of lever 167 is rotated downward. Here, the other end 167 b moves not to block the light emitted by the light emitter (not illustrated) of the photo sensor 165 and the light receiver (not illustrated) receives the light emitted by the light emitter. Thus, the front end Pt of the print paper P approaching the nip N is sensed. The photo sensor 165 generates a sensing signal corresponding to the front end Pt of the print paper P and transmits the signal to the controller 170. The controller 170 receives the sensing signal corresponding to the front end Pt of the print paper P, recognizes the time of sensing the front end Pt of the print paper P by the photo sensor 165, and then generates and transmits a driving control signal to the electronic clutch 175 so that the registration rollers 161 and 163 can be rotated after a first time-lag from the time for the sensing the front end Pt of the print paper P.

Referring to FIG. 6, the print paper P is continuously transported by the rotation of the pick-up roller 150 beginning from the time of sensing the front end Pt of the print paper P until the end of the first time-lag. The front end Pt of the print paper P is blocked by the nip N to form a curl C and is thus registered. When the first time-lag passed after the curl C of the front end Pt of the print paper P was forward, the motor (not illustrated) is connected to the first registration roller 161 via the electronic clutch 175. Then, the front end Pt of the registered print paper P passes through the nip N.

As shown in FIG. 7, when the contact surface 151 of the pick-up roller 150 is disconnected from the friction pad 147, the print paper P is not supported by the pick-up roller 150 but by the registration rollers 161 and 163. Therefore, the first time-lag elapses before the contact surface 151 of the pick-up roller 150 and the friction pad 147 are disconnected. The value of the first time-lag can be appropriately determined based on the transport speed of the print paper P toward the nip N and the distance between the one end 167 a of the lever 167 and the nip N.

Referring to FIG. 7, the controller 170 generates and transmits a pause control signal to pause the rotation of the registration rollers 161 and 163 after a second time-lag from the point of time sensing the front end Pt of the print paper to the electronic clutch 175. Accordingly, the electronic clutch 175 disconnects the registration roller 161 and 163 and the motor (not illustrated), and the transportation of the front end Pt of the print paper P passing through the nip N is discontinued towards the transfer nip Nt and on standby for printing, (see FIG. 2). The value of the second time-lag can be determined to be equal to the sum of the first time-lag and an appropriate time so that the print paper P can be firmly supported by the nip N.

After that, the controller 170 transmits a driving control signal for driving the registration rollers 161 and 163 to the electronic clutch 175 after an appropriate time-lag so that the print paper P can pass through the transfer nip Nt at the corresponding time when a visible image developed on the photosensitive medium 115 (see FIG. 2) reaches the transfer nip Nt.

FIGS. 8 through 11 are schematic views sequentially illustrating an operation of the paper registering/feeding unit 240 according to another embodiment of the exemplary embodiments of the present invention. The paper registering/feeding unit 240 can be substituted for the paper registering/feeding unit 140 installed in the image forming apparatus 100 of FIG. 2.

Referring to FIGS. 8 through 11, like the paper registering/feeding unit 140 of FIGS. 4 through 7, the paper registering/feeding unit 240 includes a paper feed cassette 241 in which sheets of print paper P are loaded, a pick-up roller 250 picking up a sheet of print paper P, a friction pad 247 contacts the pick-up roller 250 so that a sheet of print paper P is picked up, a first and second registration rollers 261 and 263 that registers and feeds the print paper P picked up to the printing unit, a photo sensor 265 that senses the approach of the print paper P, and a lever 267. In addition, the paper registering/feeding unit 240 includes a motor (not illustrated) providing a driving force to the first registration roller 261, such as a driving roller. A electronic clutch 275 selectively connects and disconnects the first registration roller 261 to and from the motor and a controller 270 controls the rotation of the registration rollers 261 and 263 with respect to a time of sensing the front end Pt of the print paper P by the photo sensor 265. The controller 270 is electrically connected to the photo sensor 265 to receive the sensing signal of the front end Pt of the print paper P from the photo sensor 265. The controller 270 is also electrically connected to the electronic clutch 275 to transmit a control signal to the electronic clutch 275 to control the rotation of the registration rollers 261 and 263.

The pick-up roller 250 includes an effective contact surface 251 contacting the print paper for transporting the paper and a detached surface 252 that does not contact the print paper P. The paper registering/feeding unit 240 does not include an additional roller for feeding the print paper P between the pick-up roller 250 and the pair of the registration rollers 261 and 263. The front end Pt of the print paper P is transported toward the nip N of the registration roller 261 and 263 by only a frictional force between the effective contact surface 251 of the pick-up roller 150 and the print paper P.

In order for the front end Pt of the picked up print paper P to reach the nip N, the arc length d1′ of the effective contact surface 251 is greater than the distance d2′ of a pathway R2 which is a portion of the entire pathway R (see FIG. 2) of the print paper. The pathway R2 is measured from the position S where the print paper P initially contacts the effective contact surface 251 during the one rotation of the pick-up roller 250 to the nip N as illustrated in FIG. 8.

Hereinafter, the operation of the registering/feeding unit 240 will be described.

When a print command is input to the image forming apparatus 100, (see FIG. 2), the pick-up roller 150 is rotated to pick up a front end Pt of the print paper P and transports the paper to reach the nip N of the registration roller 161 and 163.

When a print command is input to the image forming apparatus 100, (see FIG. 2), the pick-up roller 250 is rotated once, the effective contact surface 251 contacts the front end Pt of the print paper P to pick up the print paper P. The print paper P is directly transported to reach the nip N of the registration roller 261 and 263 by only the transportation force of the pick-up roller 250. As shown in FIG. 8, the one end 267 a of the lever 267 is positioned below the nip N and the other end 267 b of the lever 267 is positioned in the slit (not illustrated) of the photo sensor 265. Light emitted by the light emitter (not illustrated) of the photo sensor 265 is blocked by the other end 267 b and cannot reach the light receiver (not illustrated). The electronic clutch 275 disconnects the motor (not illustrated) and the first registration roller 261 according to a pause control signal transmitted by the controller 270. Therefore, the first and second registration rollers 261 and 263 do not rotate.

When the front end Pt of the print paper P is upwardly transported to push up the one end 267 a of the lever 267, as shown in FIG. 9, the lever 267 is rotated clockwise on the pivot shaft 268, and then the other end 267 b of lever 167 is rotated downward. Here, the other end 267 b moves not to block the light emitted by the light emitter (not illustrated) of the photo sensor 265 and the light receiver (not illustrated) receives the light emitted by the light emitter, thus approaching the front end Pt of the print paper P the nip N is sensed. The photo sensor 265 generates a sensing signal corresponding to the front end Pt of the print paper P and transmits the signal to the controller 270. The controller 270 receives the sensing signal corresponding to the front end Pt of the print paper P, recognizes the time of sensing the front end Pt of the print paper P by the photo sensor 265, and then generates and transmits a driving control signal to the electronic clutch 275 so that the registration rollers 261 and 263 can be rotated after a first time-lag from the time for the sensing the front end Pt of the print paper P.

Referring to FIG. 10, the print paper P is continuously transported by the rotation of the pick-up roller 250 beginning from the time of sensing the front end Pt of the print paper P until the end of the first time-lag, and the front end Pt of the print paper P is blocked by the nip N to form a curl C and thus registered. When the first time-lag passed after the curl C of the front end Pt of the print paper P was forward, the motor (not illustrated) is connected to the first registration roller 261 via the electronic clutch 275 and the front end Pt of the registered print paper P passes through the nip N.

As shown in FIG. 11, when the pick-up roller 250 is disconnected from the the print pad P, the print paper P is not transported by the pick-up roller 250 but by the registration rollers 261 and 263. Therefore, the first time-lag elapses before the effective contact surface 251 of the pick-up roller 250 and the print medium P are disconnected. The value of the first time-lag can be appropriately determined based on the transport speed of the print paper P toward the nip N and the distance between the one end 267 a of the lever 267 and the nip N.

Referring to FIG. 11, the controller 270 generates and transmits a pause control signal to pause the rotation of the registration rollers 261 and 263 after a second time-lag from the point of time sensing the front end Pt of the print paper to the electronic clutch 275. Accordingly, the electronic clutch 275 disconnects the registration roller 261 and 263 and the motor (not illustrated), and the transportation of the front end Pt of the print paper P passing through the nip N is discontinued towards the transfer nip Nt and on standby for printing, (see FIG. 2). The value of the second time-lag can be determined to be equal to the sum of the first time-lag and an appropriate time so that the print paper P can be firmly supported by the nip N.

After that, the controller 270 transmits a driving control signal for driving the registration rollers 261 and 263 to the electronic clutch 275 after an appropriate time-lag so that the print paper P can pass through the transfer nip Nt at the corresponding time when a visible image developed on the photosensitive medium 115 (see FIG. 2) reaches the transfer nip Nt.

The paper registering/feeding unit according to the exemplary embodiments of the present invention has a simple structure because it does not use additional rollers between a pick-up roller and registration rollers. Therefore, the paper registering/feeding unit has relatively high reliability, reduced manufacturing costs, and can minimize the size of an image forming apparatus.

While the present invention has been particularly shown and described with reference to exemplary embodiments thereof, it will be understood by those of ordinary skill in the art that various changes in form and details may be made therein without departing from the spirit and scope of the exemplary embodiments of the present invention as defined by the following claims. For example, the image forming apparatus including the paper registering/feeding unit of the exemplary embodiments of the present invention may be an ink jet printer or an intermediate transfer type color laser printer. Therefore, the scope of the exemplary embodiments of the present invention is defined by the following claims. 

1. A paper registering/feeding unit comprising: a rotatable pick-up roller including a contact surface which contacts a sheet of print paper to pick up the print paper; a plurality of registration rollers in contact with each other to form a nip along the pathway of the print paper; a sensor sensing the approach of the front end of the print paper picked up by the pick-up roller toward the nip of the registration rollers; and a controller that controls rotation of the registration rollers based on a time of sensing the front end of the print paper by the sensor, wherein the length of the arc of the contact surface is greater than the distance between the pick-up roller and the nip of the registration rollers along the pathway of the print paper.
 2. The paper registering/feeding unit of claim 1, wherein the controller comprises a unit that rotates the registration rollers after a first time-lag from the time of sensing the front end of the print paper so that the front end of the print paper curls, registered and passed through the nip of the registration rollers, and that pauses the registration rollers after a second time-lag from the time of sensing the front end of the registered print paper passing through the nip so that the transportation of the front end of the print paper is discontinued and on standby for printing.
 3. The paper registering/feeding unit of claim 1, wherein the paper registering/feeding unit comprises no additional rollers for feeding the print paper between the pick-up roller and the registration rollers.
 4. The paper registering/feeding unit of claim 1, wherein the paper registering/feeding unit further comprises a clutch that selectively connects and disconnects the registration rollers to and from a driving source for driving the registration roller according to control signals generated by the controller.
 5. An image forming apparatus having a printing unit that prints an image on print paper and a paper registering/feeding unit that registers and feeds the print paper to the printing unit, wherein the paper registering/feeding unit comprises: a rotatable pick-up roller including a contact surface which contacts a sheet of print paper to pick up the print paper; a plurality of registration rollers in contact with each other and forming a nip along the pathway of the print paper; a sensor sensing the approach of the front end of the print paper picked up by the pick-up roller toward the nip of the registration rollers; and a controller that controls rotation of the registration rollers based on the time of sensing the front end of the print paper by the sensor, wherein the length of the arc of the contact surface is greater than the distance between the pick-up roller and the nip of the registration rollers along the pathway of the print paper.
 6. The image forming apparatus of claim 5, wherein the controller comprises a unit that rotates the registration rollers after a first time-lag from the time of sensing the front end of the print paper so that the front end of the print paper is curled, registered and passed through the nip of the registration rollers, and that pauses the registration rollers after a second time-lag from the time of sensing the front end of the registered print paper passing through the nip so that the transportation of the front end of the print paper is discontinued and on standby for printing.
 7. The image forming apparatus of claim 5, wherein the image forming apparatus comprises no additional rollers for feeding print paper between the pick-up roller and the registration rollers.
 8. The image forming apparatus of claim 5, wherein the image forming apparatus further comprises a clutch that selectively connects and disconnects the registration rollers to and from the driving source for driving the registration roller according to control signals generated by the controller.
 9. A method of registering/feeding print paper, the method comprising: picking up and transporting the print paper toward a nip of registration rollers by rotating a pick-up roller; sensing the approach of the front end of the print paper toward the nip; driving the registration rollers after a first time-lag from a time of sensing the front end of the print paper so that the front end of the print paper is curled, registered and passed through the nip of the registration rollers; and pausing the registration rollers after a second time-lag from the time of sensing the front end of the print paper toward the nip so that the transportation of the front end of the print paper registered and passed through the nip is discontinued and on standby for printing.
 10. The method of claim 9, wherein, in the transporting of the print paper, the print paper is directly transported to the nip of the registration rollers by only the transportation force of the pick-up roller.
 11. A paper registering/feeding unit comprising; a rotatable pick-up roller including an effective contact surface which contacts a sheet of print paper to pick up the print paper; a pair of registration rollers in contact with each other to form a nip along the pathway of the print paper; a sensor sensing the approach of the front end of the print paper picked up by the pick-up roller toward the nip of the registration rollers; and a controller that controls rotation of the registration rollers based on a time of sensing the front end of the print paper by the sensor, wherein the length of the arc of the effective contact surface is greater than the distance from the position where the pick-up roller initially contacts the print paper to the nip of the registration rollers along the pathway of the print paper.
 12. The paper registering/feeding unit of claim 11, wherein the controller comprises a unit that rotates the registration rollers after a first time-lag from the time of sensing the front end of the print paper so that the front end of the print paper is curled, registered and passed through the nip of the registration rollers, and that pauses the registration rollers after a second time-lag from the time of sensing the front end of the registered print paper passing through the nip so that the transportation of the front end of the print paper is discontinued and on standby for printing.
 13. The paper registering/feeding unit of claim 11, wherein the paper registering/feeding unit comprises no additional rollers for feeding print paper between the pick-up roller and the registration rollers.
 14. The paper registering/feeding unit of claim 11, wherein the image forming apparatus further comprises a clutch that selectively connects and disconnects the registration rollers to and from the driving source for driving the registration roller according to control signals generated by the controller.
 15. An image forming apparatus having a printing unit that prints an image on print paper and a paper registering/feeding unit that registers and feeds the print paper to the printing unit, wherein the paper registering/feeding unit comprises: a rotatable pick-up roller including an effective contact surface which contacts a sheet of print paper to pick up the print paper; a pair of registration rollers in contact with each other to form a nip along the pathway of the print paper; a sensor sensing the approach of the front end of the print paper picked up by the pick-up roller toward the nip of the registration rollers; and a controller that controls rotation of the registration rollers based on a time of sensing the front end of the print paper by the sensor, wherein the length of the arc of the effective contact surface is greater than the distance from the position where the pick-up roller initially contacts the print paper to the nip of the registration rollers along the pathway of the print paper.
 16. The image forming apparatus of claim 15, wherein the controller comprises a unit that rotates the registration rollers after a first time-lag from the time of sensing the front end of the print paper so that the front end of the print paper is curled, registered and passed through the nip of the registration rollers, and that pauses the registration rollers after a second time-lag from the time of sensing the front end of the registered print paper passing through the nip so that the transportation of the front end of the print paper is discontinued and on standby for printing.
 17. The image forming apparatus of claim 15, wherein the image forming apparatus comprises no additional rollers for feeding print paper between the pick-up roller and the registration rollers.
 18. The image forming apparatus of claim 15, wherein the image forming apparatus further comprises a clutch that selectively connects and disconnects the registration rollers to and from the driving source for driving the registration roller according to control signals generated by the controller. 